signal/x86: Move mpx siginfo generation into do_bounds

This separates the logic of generating the signal from the logic of
gathering the information about the bounds violation.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

arch/x86/include/asm/mpx.h

@@ -57,8 +57,14 @@
 #define MPX_BNDCFG_ADDR_MASK	(~((1UL<<MPX_BNDCFG_TAIL)-1))
 #define MPX_BNDSTA_ERROR_CODE	0x3
 
+struct mpx_fault_info {
+	void __user *addr;
+	void __user *lower;
+	void __user *upper;
+};
+
 #ifdef CONFIG_X86_INTEL_MPX
-siginfo_t *mpx_generate_siginfo(struct pt_regs *regs);
+int mpx_fault_info(struct mpx_fault_info *info, struct pt_regs *regs);
 int mpx_handle_bd_fault(void);
 static inline int kernel_managing_mpx_tables(struct mm_struct *mm)
 {
@@ -78,9 +84,9 @@ void mpx_notify_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
 unsigned long mpx_unmapped_area_check(unsigned long addr, unsigned long len,
 		unsigned long flags);
 #else
-static inline siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
+static inline int mpx_fault_info(struct mpx_fault_info *info, struct pt_regs *regs)
 {
-	return NULL;
+	return -EINVAL;
 }
 static inline int mpx_handle_bd_fault(void)
 {

arch/x86/kernel/traps.c

@@ -455,7 +455,6 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 {
 	const struct mpx_bndcsr *bndcsr;
-	siginfo_t *info;
 
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 	if (notify_die(DIE_TRAP, "bounds", regs, error_code,
@@ -493,8 +492,11 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 			goto exit_trap;
 		break; /* Success, it was handled */
 	case 1: /* Bound violation. */
-		info = mpx_generate_siginfo(regs);
-		if (IS_ERR(info)) {
+	{
+		struct mpx_fault_info mpx;
+		struct siginfo info;
+
+		if (mpx_fault_info(&mpx, regs)) {
 			/*
 			 * We failed to decode the MPX instruction.  Act as if
 			 * the exception was not caused by MPX.
@@ -508,9 +510,16 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 		 * allows and application to possibly handle the
 		 * #BR exception itself.
 		 */
-		do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, info);
-		kfree(info);
+		clear_siginfo(&info);
+		info.si_signo = SIGSEGV;
+		info.si_errno = 0;
+		info.si_code  = SEGV_BNDERR;
+		info.si_addr  = mpx.addr;
+		info.si_lower = mpx.lower;
+		info.si_upper = mpx.upper;
+		do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, &info);
 		break;
+	}
 	case 0: /* No exception caused by Intel MPX operations. */
 		goto exit_trap;
 	default:

arch/x86/mm/mpx.c

@@ -118,14 +118,11 @@ static int mpx_insn_decode(struct insn *insn,
  * anything it wants in to the instructions.  We can not
  * trust anything about it.  They might not be valid
  * instructions or might encode invalid registers, etc...
- *
- * The caller is expected to kfree() the returned siginfo_t.
  */
-siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
+int mpx_fault_info(struct mpx_fault_info *info, struct pt_regs *regs)
 {
 	const struct mpx_bndreg_state *bndregs;
 	const struct mpx_bndreg *bndreg;
-	siginfo_t *info = NULL;
 	struct insn insn;
 	uint8_t bndregno;
 	int err;
@@ -153,11 +150,6 @@ siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
 	/* now go select the individual register in the set of 4 */
 	bndreg = &bndregs->bndreg[bndregno];
 
-	info = kzalloc(sizeof(*info), GFP_KERNEL);
-	if (!info) {
-		err = -ENOMEM;
-		goto err_out;
-	}
 	/*
 	 * The registers are always 64-bit, but the upper 32
 	 * bits are ignored in 32-bit mode.  Also, note that the
@@ -168,27 +160,23 @@ siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
 	 * complains when casting from integers to different-size
 	 * pointers.
 	 */
-	info->si_lower = (void __user *)(unsigned long)bndreg->lower_bound;
-	info->si_upper = (void __user *)(unsigned long)~bndreg->upper_bound;
-	info->si_addr_lsb = 0;
-	info->si_signo = SIGSEGV;
-	info->si_errno = 0;
-	info->si_code = SEGV_BNDERR;
-	info->si_addr = insn_get_addr_ref(&insn, regs);
+	info->lower = (void __user *)(unsigned long)bndreg->lower_bound;
+	info->upper = (void __user *)(unsigned long)~bndreg->upper_bound;
+	info->addr  = insn_get_addr_ref(&insn, regs);
+
 	/*
 	 * We were not able to extract an address from the instruction,
 	 * probably because there was something invalid in it.
 	 */
-	if (info->si_addr == (void __user *)-1) {
+	if (info->addr == (void __user *)-1) {
 		err = -EINVAL;
 		goto err_out;
 	}
-	trace_mpx_bounds_register_exception(info->si_addr, bndreg);
-	return info;
+	trace_mpx_bounds_register_exception(info->addr, bndreg);
+	return 0;
 err_out:
 	/* info might be NULL, but kfree() handles that */
-	kfree(info);
-	return ERR_PTR(err);
+	return err;
 }
 
 static __user void *mpx_get_bounds_dir(void)